There currently exists a number of methods and systems for the selective separation of gaseous feed streams, including, for instance, the removal of olefins from gas streams containing olefin and paraffin components. Transition metals such as copper, cobalt, nickel, manganese and silver have long been known to coordinate with unsaturated chemical species. This chemistry has been used extensively in synthesis, catalysis and analysis.
The utility of liquid membranes exploiting this coordination chemistry as a functional means of separating gases from one another is also known in the art. For instance, U.S. Pat. Nos. 3,758,603 and 3,758,605 describe the use of aqueous liquid membranes containing silver nitrate and supported on a variety of porous polymeric supports for the separation of olefins such as ethylene and propylene from paraffins such as methane and ethane.
Different liquid membrane systems have been used to accomplish other types of separations. For instance, it is known to use a cation-exchange membrane containing protonated ethylenediamine cations to separate CO.sub.2 from various gas streams. This has again, however, entailed the use of an aqueous-based liquid membrane. There are inherent problems with the known, aqueous liquid membrane separation systems. One is that the constant exposure of the membrane to flowing gas streams necessitates the humidification of the streams to prevent the membrane from drying out, thereby destroying its utility. Another is that an aqueous system limits the range of facilitators capable of being used to those that are water soluble. Still another is that membrane support materials, such as polysulfone, are often hydrophobic, and are difficult to wet and even more difficult to maintain wetted. Drying out of the polymer support results in open channels that allow the permeation of the unseparated feed gas stream, at best resulting in severe drops in permeate purity.
Due to the inherent problems with aqueous membrane systems, an organic liquid membrane might be considered as advantageous. Nevertheless, not all organic solvents can be used for membrane based gas separations. Organic solvents such as ethylene glycol, glycerol and DMSO have proven to be less than desirable, as all yield olefin permeabilities much lower than those of their aqueous counterparts.
Therefore, a need exists for a liquid membrane system employing a liquid component which is resistant to membrane dry-out and which will eliminate the need for humidified gas streams. The liquid component should have viscosities and dielectric constants comparable to those of water, in order to take advantage of current support component technology.